The U.S. is accusing North Korea of breaching U.N. sanctions on the import of refined petroleum via illegal ship-to-ship transfers -- a move that marks a contrast to the warmer rhetoric directed at the North Korean regime coming from the White House.

A Security Council diplomat told reporters late Wednesday that the U.S., along with 25 other countries, had complained to the U.N. Security Council sanctions committee monitoring the country’s compliance with sanctions slapped on the country in 2017.

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The complaint, first reported by Bloomberg News, said that the North Koreans blew past the annual limit of 500,000 barrels of refined petroleum products in 2018 and were on track to do the same in 2019. The diplomat said that while it was difficult to know how much refined petroleum North Korea had smuggled in, they estimated that it was approximately 3.5 million barrels in 2018.

The U.S. had issued a similar complaint last year but it was blocked by the Russians and the Chinese. The diplomat said the U.S. is more hopeful this year as it has a significant number of countries signing on to the document, both Russia and China were informed of the move ahead of time, and the submitted report includes significantly more evidence and detail about the claims made within it.

Security Council countries have until Tuesday to object to the sanctions committee taking action and can place a hold on a decision for up to nine months. The diplomat said that it is not seeking to increase or expand sanctions on North Korea, but merely to implement existing ones.

The escalation in tensions at the U.N. comes even as President Trump has continued to speak warmly of his relationship with North Korean dictator Kim Jong Un.

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Trump, who once spoke of unleashing “fire and fury” against the North Koreans in 2017 if they continued missile testing, has taker a gentler tone with the tyrant since their two summits in 2018 and 2019.

He said this week he received “a beautiful letter” from Kim and shrugged off a Wall Street Journal report that Kim’s half-brother was a CIA source, telling reporters he would tell Kim that he “would not let that happen under my auspices.”

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But the U.S. has been questioning North Korea’s adherence to U.N. demands for a while. National Security Adviser John Bolton said last month that there was “no doubt” that recent short-term missile launches by the country were in violation of U.S. Security Council resolutions.

"U.N. Security Council resolutions prohibit North Korea from firing any ballistic missiles," Bolton told reporters in Tokyo. "In terms of violating U.N. Security Council resolutions, there is no doubt about that."

Fox News' Ben Evansky contributed to this report.